Native to the sunny mountain valleys across China and Japan, heavenly bamboo (Nandina domestica) grows as an upright, multistemmed shrub with evergreen or semievergreen foliage. Regular selections of heavenly bamboo readily mature 5 to 6 feet tall and up to 5 feet wide. By contrast, more modern dwarf varieties range in mature height from 14 inches to 4 feet tall. All these shrubs may be pruned, but with thought and precision, as once the stem is cut off, no further upward growth occurs. Carefully prune dwarf varieties in spring.
Pruning Time Frame
Prune dead or broken branches anytime. Because dwarf heavenly bamboo naturally remains small and is slow growing, incorrect pruning is easily noticed because of the loss of foliage, stems and overall plant lushness. Typically, little or no pruning is needed on the more compact, tidy-shaped dwarf cultivars. The best time to prune living tissues is in mid- to late spring when new growth starts and you can select which branches to retain for a more attractive plant by midsummer.
What to Prune
Do not arbitrarily cut the tops of stems on any heavenly bamboo plant. You not only remove the natural leaf clusters, but also the areas yielding the white flowers and subsequent red berry clusters. Only prune the tallest or least vigorous-looking stems from the plant clump. This is described as thinning out the number of upright stems. Make the pruning cuts flush with the soil or at a height below the tops of other stems at a height you like. For example, if one errant stem stands 24-inches tall with all others only 18-inches tall, cut that lone stem back to the ground or any height below 18 inches. Avoid cutting it off right at 18 inches, as the pruning stub is visible at the top of the plant.
Heavenly bamboo dwarf cultivars may be severely cut back for rejuvenation. After several years of growth, the thicket of stems and leaves may cause the plant to look tired or lack lush, attractive foliage. An unusually cold winter may kill leaves and stems by early spring. Rejuvenate such dwarf heavenly bamboo plant but cutting back the entire plant to the ground or stubs 1 to 3 inches tall in very early spring. New growth appears from the roots across the warmer months of spring and into summer.
Pruning heavenly bamboo shrubs is not a maintenance practice required annually. Trim occasionally errant stems to maintain uniformity in the plant. Rejuvenation is best done only once every 5 to 10 years. Unhealthy plants are not good candidates for rejuvenation. Infertile or dry soils and windy sites stress heavenly bamboo and do not encourage the best regrowth or as rapid of rejuvenation, compared to plants growing in an evenly moist, fertile soil in sheltered, sunny conditions.